Alright, for one the 6600GT could easily and totally destroy the 5700, there's really no contest dude, so that's a really nice card, best in it's class. Sadly if you didn't upgrade you're motherboard to one that supports PCI-Express you can't use the 6600GT you picked out, however they do offer AGP versions for about $20 more or so. If you're concerned about the smaller vram size, don't it may seem like a major factor but the shear power of the 6600GT will more than make up for it (expecially if you had to in SLI). Hope this helps mate.